The present invention relates, in general, to manufacturing semiconductor devices, and more particularly to manufacturing of semiconductor devices which emit light.
This application is related to U.S. Pat. No. 5,034,092, entitled "Plasma Etching of Semiconductor Substrates", by M. Lebby et al., assigned to Motorola Inc., which is incorporated herein by reference. M. Lebby is co-inventor of the present invention which is also assigned to Motorola Inc.. The related patent teaches a fabrication method used in a structure which is superficially similar to that of the present invention. The earlier device, however, was fabricated as a vertical cavity surface emitting laser (VCSEL) rather than a superluminescent surface light emitting device.
Superluminescent light-emitting devices combine high efficiency with a broad spectral bandwidth. These characteristics are important for achieving high performance in applications such as a light source for fiber-optic gyroscopes. Another application for such devices is in a display matrix in which light from several hundred devices is combined to form an image. Light emitting diodes have low efficiency, but light from lasers combines to produce an undesirable "speckle" effect in an image due to coherent wave interference. The broad spectral bandwidth of a superluminescent light-emitting device precludes coherent wave interference effects.
Production of light through the surface of a semiconductor device is highly desirable. Such devices have the potential to be incorporated within an integrated circuit chip having other functions. Also, large arrays of similar such devices may be fabricated on a single substrate to provide an economical, high efficiency, planar display. A surface emitting device may be assembled easily by direct mounting onto a substrate rather than requiring a difficult "flip" mounting. Testing of the device before separation of the wafer into individual chips is possible. This pre-separation testing avoids the need to mount and package defective devices which must then be scrapped. Since packaging costs are a major component of the total device cost both the ease of assembly and pre-separation testing represent significant manufacturing cost reductions. Studies of defect locations on a wafer often provides valuable information which may be used to optimize a wafer manufacturing process. This valuable manufacturing information cannot be obtained if the wafer must be separated into chips before testing. Finally, the finished device will exhibit improved reliability since the critical junction regions are sealed within the structure.
Superluminescent devices provide high efficiency and freedom from wave interference effects, surface light emitting devices facilitate economical manufacturing, testing and packaging. There is a need for a device which combines the advantages of surface light emission with the unique advantages of superluminescence.